In optical communication networks, optical superchannels are used to transmit multiple optical signal streams on several subchannels (wavelength subchannels) which are closely spaced to each other. To make best use of the available bandwidth the exact frequency spacing of the subchannels needs to be actively controlled. In this scenario, the optical transmitter uses Nyquist pulse shaping to allow for dense channel spacing.
In a coherent optical network, the optical signals on each wavelength are amplitude and phase modulated and polarization multiplexing is used to further increase throughput. A receiver uses coherent optical reception in conjunction with analog-to-digital conversion to linearly translate the received optical field to electrical signals. The electrical signals are then converted to digital signals and further processed using digital signal processing algorithms. The optical receiver is capable of receiving several (e.g., ten) neighboring channels without having to use an optical channel selection filter.